12V battery lithium replacement build

I got a crate full of old 18650 lithium cells from Nelius a while back and thought I would share one of the battery builds I used these for.

Our local squash club use magnetic locks for the access doors and the old 12V lead acid batteries did not last more than 15min anymore. So these need to be replaced.

I found a 10A/60A BMS that has seperate charge and discharge ports. This way if the BMS stops the charging it would not open the door on the seperate output.

I picked 24 cells that all had similar capacities of around 2Ah each and used some 18650 spacers to put them all together 3S8P for a total of 16Ah at 11.1V

The cells were wired up using nickel strips spot welded together, and then I used my smart charger to slowly charge the cells to capacity, giving the balancer circuitry time to work to get all the cells top balanced.

Last part was to wire in the actual charger, setting the voltage and then testing that is all worked fine. The 100W charger should be able to charge the battery in under 2 hours.

It’s been installed a few weeks now and I’m glad to say the door stay shut even on the 4 hour power cuts we had on level 6 loadshedding (the battery was designed to keep the 2 doors shut for ~9hours.


I really want to do this for a 96V (8x 7ah) 2kVA rackmount UPS I have, but it seems scary complicated :slight_smile:

Well done.

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If you don’t find a 96V BMS it will be a bit more challenging.
I have a friend with a 6x7Ah UPS, but I could also not find a 72V BMS. Building it with 12V packs and taking it appart to balance every few months also is not really the install and forget I had in mind.

Yeah, then I can just as well use 7ah replacements, but it gets expensive.

Maybe this one?
IF I’m right, 72v / 3.6 = 20 cells
Max it can do is 3.75v x 20 = 75v